Question
The vasa recta and loop of Henle flow in ____ directions, creating a countercurrent multiplier system that allows maximal reabsorption of water.
Answer
The vasa recta and loop of Henle flow in opposite directions, creating a countercurrent multiplier system that allows maximal reabsorption of water.
Note: The vasa recta blood network that surrounds the loop of Henle flows in the opposite direction (counter-current).
Note: Countercurrent multiplication in the kidneys is the process of using energy to generate an osmotic gradient that enables you to reabsorb water from the tubular fluid and produce concentrated urine. This mechanism prevents you from producing litres and litres of dilute urine every day, and is the reason why you don’t need to be continually drinking in order to stay hydrated.
Huge Note: The term, countercurrent multiplier, derives from the form and function of the loop of Henle, which consists of two parallel limbs of renal tubules running in opposite directions, separated by the interstitial space of the renal medulla.
- The descending limb of the loop of Henle is permeable to water but impermeable to solutes, due to the presence of aquaporin 1 in its tubular wall. Thus, water moves across the tubular wall into the medullary space, making the filtrate hypertonic (with a lower water potential). This is the filtrate that continues to the ascending limb.[2]
- The ascending limb is impermeable to water (because of a lack of aquaporin, a common transporter protein for water channels in all cells except the walls of the ascending limb of the loop of Henle) but permeable to solutes, but here Na+, Cl−, and K+ are actively transported into the medullary space, making the filtrate hypotonic (with a higher water potential). The interstitium is now "salty" or hypertonic, and will attract water as below. This constitutes the single effect of the countercurrent multiplication process.[3]
- Active transport of these ions from the thick ascending limb creates an osmotic pressure drawing water from the descending limb into the hyperosmolar medullary space, making the filtrate hypertonic (with a lower water potential).[4]
- The countercurrent flow within the descending and ascending limb thus increases, or multiplies the osmotic gradient between tubular fluid and interstitial space.
Keep this card coming back until it sticks
Sign up free and spaced repetition will bring MilesDown: Biology cards back right before you forget them.
Continue studying — sign up free